At present, to examine the processing accuracy and the like of a three-dimensional product, shape measuring apparatuses having a three-dimensional measuring machine 1 as shown in FIG. 1 and the like are used. Such a three-dimensional measuring machine 1 measures the shape of a product A by, for example, moving a tip ball 14 of a stylus 12 of a scanning probe 10 along the three-dimensional shape of the product A. In the drawing, a reference numeral 2 refers to a column. A reference numeral 3 refers to a movable table. A reference numeral 4 refers to a base. A reference numeral 5 refers to a support frame. A reference numeral 6 refers to a brace. A reference numeral 7 refers to a beam. A reference numeral 8 refers to a slider.
When the three-dimensional measurement machine 1 performs measurement using the scanning probe 10, a measurement error occurs by the effect of the operation of the slider 8 to which the scanning probe 10 is attached. For example, in measuring a circle by the scanning probe 10, a motion error called a quadrant projection occurs. The quadrant projection is a motion error formed into a projection at the time of mechanically switching quadrants (at the time of reversing a movement direction of each axis) in rectangular coordinates of the three-dimensional measuring machine 1, when the tip ball 14 of the stylus 12 of the scanning probe 10 is in circular motion. This quadrant projection is mainly caused by a backlash and the like owing to the mechanical structure of the three-dimensional measuring machine 1.
FIG. 3 shows an example of a result of scanning measurement of an arc C of a sphere B, being an object to be measured, in a stylus position as shown in FIG. 2. A measurement error due to the quadrant projection at the time of switching from a fourth quadrant to a first quadrant is especially prominent. This is an error caused by the quadrant projection produced by a backlash and the like in reversing movement of the scanning probe 10.
On the other hand, Japanese Patent No. 5221004 (hereinafter called Patent Literature 1) describes an example of a correction method of the measurement error occurring in measurement using the scanning probe 10. According to this method, the position of a slider tip at an end of the slider is estimated with the use of a correction filter based on a frequency transfer characteristic between a scale unit for detecting a displacement of the slider and the slider tip. Then, a measurement value is calculated by adding an estimated value to a scanning probe detection value, so that the measurement error owing to the quadrant projection can be corrected.
Japanese Patent Application Laid-Open No. 2014-66693 (hereinafter called Patent Literature 2) and Japanese Patent Application Laid-Open No. 2014-98610 (hereinafter called Patent Literature 3) also describe correction methods of the measurement error owing to the quadrant projection.